It's not just that Apple designed a good small speaker--it has 17 tweeters, for example--but that it's actually a "smart" speaker from the point of view of speakers. That is to say, it listens to its own output, then adjusts itself to sweeten the sound.

Apparently, it also works in pairs, though I don't see any mention that it knows it's part of a pair and becomes a stereo pair.

"Design is not just what it looks like and feels like. Design is how it works."
Steve Jobs